Information is transmitted over computer networks. The information is represented as bits grouped into packets. The packets are passed from network device to network device, e.g., switches and routers, propagating the information through the computer networks. Each packet is transmitted from its source towards a destination specified by header information in the respective packet. The source and destination of a packet may respectively be in different portions of the network, each portion operated by a different party. There may be multiple possible routes between the source and destination.
A wide area network (“WAN”), such as the Internet, can include multiple sub-networks known as autonomous systems (“AS”). An autonomous system is a portion of the network that appears to other portions of the network as though it has unified administration of a single routing policy and presents, to the other portions of the network, a consistent picture of reachable network destinations, e.g., as network address spaces reachable through the AS. In some instances, an autonomous system can be identified by an autonomous system number (“ASN”) that is unique within the network. Typically, an operator of an autonomous system has agreements with third-parties for allowing data to be carried on one or more autonomous systems controlled by the respective third-party, usually under a “settlement” agreement for transit billed by usage or as a “settlement-free” peering agreement. Data may then be transmitted from one autonomous system to another at a peering point, a multi-homed network device, an Internet eXchange Point (“IXP”), or the like, within the confines of the agreements between autonomous system operators. Network devices in the WAN can then communicate across a network route that may span multiple autonomous systems.